Engine Build

[TobyB]

There was a run of BMW rod bolts that couldn't take 7500 rpm.  This was maybe 20 years back, before

ARP started making them.  So a number of us stopped changing rod bolts, as the old ones were good 

to 8K and beyond.  

 

Now, it may be just residual paranoia, but it's just so easy to buy the ARP bolt and never think about it again.

 

And Ken, this was 15 years back, and I really questioned the Ross numbers, which I recall being around 0.0015- 0.0020.

But I don't remember what alloy they were.

 

t

once bitten...

Edited September 22, 2019 by TobyB

[Wilbur25]

So for this Ive decided 1mm oversize will be good as my cylinder walls need a bit of boring. I have found the Mahle oversize pistons but still cannot confirm if the small step on the top will work with the 121 head. Can anyone confirm if this step would cause any interference with the valves?  These say they are for the 121 head and for a 10:1 compression. It is either hope for the best with these pistons or go for the expensive IE forged pistons for 650$, which, I would rather save a bit of money as I will not be doing any forced induction.

 

https://www.ebay.com/itm/NEW-BMW-E10-2002tii-2-0L-L4-1971-1974-Piston-90-015-mm-1-00-mm-Over-Size-Mahle/282694185631?hash=item41d1e2f29f:g:idcAAOSw3Ohck9yj

 

Should I bite the bullet and go for the flat top IE forged pistons, or can I feel pretty safe with the small steps added onto the each piston head?

 

I will post whichever I choose for future reference if someone else is in this situation.

[tme]

On 9/19/2019 at 1:00 PM, TobyB said:

 

I too would spend the hardly-any-more- money for a set of ARP rod bolts.

 

t

Welcome to the “hardly-any-more” world of engine building.  I would use the same HAM logic ($90) and go with the IE forged pistons.  Tell IE what head you are using, bore size, cam, desired compression and they will eliminate all the guess work.  Well worth the HAM.  I did and received very nice pistons and a detailed clearance/spec sheet.  

[kbmb02]

13 hours ago, Wilbur25 said:

So for this Ive decided 1mm oversize will be good as my cylinder walls need a bit of boring. I have found the Mahle oversize pistons but still cannot confirm if the small step on the top will work with the 121 head. Can anyone confirm if this step would cause any interference with the valves?  These say they are for the 121 head and for a 10:1 compression. It is either hope for the best with these pistons or go for the expensive IE forged pistons for 650$, which, I would rather save a bit of money as I will not be doing any forced induction.

 

https://www.ebay.com/itm/NEW-BMW-E10-2002tii-2-0L-L4-1971-1974-Piston-90-015-mm-1-00-mm-Over-Size-Mahle/282694185631?hash=item41d1e2f29f:g:idcAAOSw3Ohck9yj

 

Should I bite the bullet and go for the flat top IE forged pistons, or can I feel pretty safe with the small steps added onto the each piston head?

 

I will post whichever I choose for future reference if someone else is in this situation.

 

The piston in that link appears to be correct for the 121 cylinder head. As for feeling "pretty safe", you'll feel really safe you check clearance during assembly (piston to head, piston to valve) during assembly. -KB

[rcf925]

I went with some custom Racetek forged pistons for my E12 head, Plenty of valve clearance. Balanced, Studded mains, 9:8 compression  .292 Cam, Ported head, weber 45's  . I'm happy with results, Plenty of low and mid-range torque and revs easily

 

Edited October 12, 2019 by rcf925

[xr4tic]

12 hours ago, tme said:

Welcome to the “hardly-any-more” world of engine building.  I would use the same HAM logic ($90) and go with the IE forged pistons.  Tell IE what head you are using, bore size, cam, desired compression and they will eliminate all the guess work.  Well worth the HAM.  I did and received very nice pistons and a detailed clearance/spec sheet. 

 

I'm more the WYIT type (While You're In There)

 

If you go for aftermarket pistons, consider longer rods as well.  Read up on Bore/Stroke ratio benefits to see if it's worth it for you.  Most aftermarket rods come with ARP bolts.

 

I also recommend replacing the timing chain and gears, because you've got it all apart.  I went to a single row setup, it was cheaper and in theory less rotating drag. because racecar

 

Oh yeah, oil pump chain as well, but you'll want to get the BMW part, the aftermarket pieces are known to be the wrong size.

 

Here's my blog entry with some of the stuff I did:

 

[TobyB]

Yes, those Mahle will fit the head.

 

Yes, you will want to check valve clearance with ANY piston, as Ken says.

It's as much about the valvetrain timing as anything else.

 

For a mild engine, I would stay with a cast stock piston.

 

fwiw,

t